Gas mileage ... 48 to 50 mpg US, for the last 2 years. 17 to 18 litres per refill ... tank volume supposedly at 29 litres ... about 225 miles per refill.

I do not have numbers for my last 1 or 2 refills, but nothing out of the ordinary or I would have noticed.

Spark plugs ... are you talking about the white colored ceramic like material?
In any case, I plan to replace all 4 plugs. I always use OEM.

Gas filter ... could be the culprit, considering I have put in 100 000 miles in 9 riding seasons. But if you consider that I had 4 incidents, and that between incidents 1 and 2 and 2 and 3, I put over 1000 miles in each case without the slightest symptom, I wonder. In each case, riding 2 up fully loaded, and I mean loaded, side bags and top case, cruising at 55 to 70 mph with occasional rushes at close to 90 mph, wiitout the slightest hesitation?

Original filter in ... but since it doesn't seem like such a big deal, will change the filter.

Fuel pump? Don't know ... except for the incidents, seems to pump OK.

Electrically speaking, I believe that there is only one relay in the fuel system, the fuel cut-off relay ... seems easy enough to check and replace ... will do.

If that doesn't work ... and unless someone comes up with a brilliant idea, will take the covers off and dig into the électrical wiring ... not a fun prospect.

Your problem sounds a lot like my issue I had a few months ago, it started developing as an occasional stalling jerking issue until we could not ride the bike no more, changing these burned connectors solved the situation, look at my post "Engine shuting down and odd behavior" in this section, hope it will help you if this is the case.

Ended up buying a used harness for $50 USD (on e-bay) and having my local Honda dealer swapping this burned terminals...all good so far!!